A three-year-old boy who died in the back of Toyota Corolla had allegedly been left in the car all day before his distraught father smashed a window to try and save him.
Police and paramedics rushed to Railway Parade at Glenfield, in Sydney's south-west, at about 3pm on Thursday as temperatures soared to 34C.
Detectives are investigating claims the dad dropped his oldest son off at school in the morning - but forgot to take his youngest child to childcare.
He was asleep in the back of the car, a Bangladeshi migrant community source claimed.
According to the source, the dad then spent the day busily completing tasks in his home office, under the mistaken belief his son was at childcare.
The dad allegedly didn't realise his little boy was still in the car until after he returned to the car in the afternoon to pick up his kids.
Witnesses said the desperate father punched a hole in the back window of the car and tried to retrieve his son after he found him unconscious.
He couldn't be saved.
The father was taken to Campbelltown Police Station and questioned by detectives but has since been released without charge.
'Officers from Campbelltown City Police Area Command were told the child had been in the vehicle throughout the day,' a NSW Police spokesperson said.
The boy is understood to have been taken into a nearby bottle shop where members of the public tried to resuscitate him before police arrived.
Footage from the scene showed distraught people on the ground near the car.
The father was seen covering his face as he sobbed, with blood running down his right hand.
A worker at a nearby grocery store said the father was a regular customer.
More than 5000 children are rescued from hot cars in Australia every year - the majority being babies and toddlers, according to child safety advocates Kidsafe.
'Leaving children unattended in a car - even for a short period of time - can be fatal,' reads information on Kidsafe's website .
'Children are particularly at risk because they can lose fluid quickly, become dehydrated and suffer from heatstroke.'
In December 2015, celebrity chef Matt Moran called media to a cooking demonstration at Sydney's Bondi Beach where he'd prepared a piece of lamb using just the interior heat of a parked car.
'This has been in there for a little over an hour and a half,' said Mr Moran, slicing open the meat in a video of the demonstration, 'that to me is overdone.'
What happens to children left in hot cars?
Children's bodies heat up three-to-five times faster than adults do
The younger the child, the more vulnerable they are
On a 29C day, temperatures inside a car can reach 44C in just ten minutes
This can cause 'serious injury' and brain damage
After 20 minutes, the temperature reaches a fatal 60.2C, which could kill
Winding down the windows or parking in the shade will do little as it doesn't affect the car's core temperature
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